Sperm cells can survive inside a woman's reproductive organs for five days. An egg cell can survive for one day after ovulation. In one woman ovulation occurred on day 14. Give the range of days on which sexual intercourse could result in fertilisation.

Fertilisation can only occur if live sperm and a live egg are present at the same time. - The egg is released on day 14 and survives for one day, so it is viable on day 14 and day 15. - Sperm can survive for 5 days. To find the fertile window: - The last day intercourse can lead to fertilisation is day 15, when the egg is still viable. - To find the first day, we count back 5 days from when the egg is first available (day 14). However, it is simpler to think that sperm from intercourse on day 10 will survive until day 15 (10+5=15). Sperm from day 9 would die on day 14, so might just miss the egg if it is released late on day 14. AQA mark schemes typically accept Day 9 or 10 as the start. Let's use the most common interpretation: sperm must be alive on Day 14. Intercourse on Day 10 means sperm is alive on days 10, 11, 12, 13, 14. So Day 10 is the start. The range is therefore from day 10 to day 15 inclusive.